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Michael C Bull - One of the best experts on this subject based on the ideXlab platform.
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the impact of heavy grazing on Burrow choice in the pygmy bluetongue lizard tiliqua adelaidensis
Wildlife Research, 2011Co-Authors: Melissa Pettigrew, Michael C BullAbstract:Context Grazing pressure has directly altered and indirectly influenced natural ecosystems worldwide, and has affected and displaced many native species. The endangered pygmy bluetongue lizard Tiliqua adelaidensis is endemic to the mid-north of South Australia. It inhabits remnant native grasslands where it is reliant on the presence of natural spider Burrows constructed by lycosid and mygalomorph spiders as refuge sites. These lizards spend the majority of the day associated with their Burrow either in the Burrow itself or basking at its entrance. The remnant native grasslands of South Australia have endured 200 years of agricultural changes and the introduction of domestic stock has meant that grazing pressure has substantially increased. The vegetation around a Burrow is considered to be important in providing shelter for the lizard. However, too much vegetation may reduce basking opportunities and visibility of prey. Stock grazing has been maintained on the majority of sites that contain pygmy bluetongue populations and it is presumed that the lizards can tolerate some form of grazing. However, the level of grazing intensity directly influences the vegetation structure that surrounds the lizard Burrows. Aims We aimed to investigate the consequences of severe grazing pressure on the choice of Burrows by lizards, and on their Burrow related behaviour. Methods We simulated heavy grazing pressure by manually removing aboveground vegetation in the field in replicated quadrats that contained artificial Burrows, and by providing bare substrate in half of experimental enclosures in the laboratory. Key results In the field, lizards only occupied the artificial Burrows in control quadrats, where vegetation had been left intact. In the laboratory, lizards that occupied both Burrows basked for longer at the Burrow entrance where vegetation was present. Conclusions Heavy grazing management that results in the majority of vegetation being removed could have a negative impact on pygmy bluetongue lizard recruitment and sustainability. Implications Grazing regimes should be carefully monitored to consider the needs of species that rely heavily on microhabitat structure for their persistence. For the endangered pygmy bluetongue lizard, heavy grazing should be avoided to promote amounts of vegetation suitable to sustain viable populations.
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adding Burrows to enhance a population of the endangered pygmy blue tongue lizard tiliqua adelaidensis
Biological Conservation, 2004Co-Authors: Nicholas J Souter, Michael C Bull, Mark N HutchinsonAbstract:The endangered pygmy blue tongue lizard, Tiliqua adelaidensis, occupies spider Burrows in a population near Burra, South Australia. In each of twelve 20 × 20 m plots at that population, we added 36 artificial Burrows, providing about a ten fold increase in suitable Burrows for lizards. Over three surveys during the spring and summer of 2001/2002 there were significant increases in lizard numbers in the experimental plots relative to the controls, both for adult lizards and for new recruits after clutches were produced. This local increase in population density may be due to lizards locating suitable Burrows more easily where Burrow numbers were supplemented. The increased availability of high quality Burrows may also reduce mortality among lizards searching for suitable Burrows. Additional Burrows also led to an increase in local density of a Burrow-dwelling centipede that is a potential predator of lizards, but there was no evidence of predation, and any negative predation impact was outweighed by the beneficial effect of providing more Burrows. Overall the results suggest that adding artificial Burrows could enhance local population density and recruitment success, and that this could be a valuable tool in the conservation management of this endangered species.
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use of Burrows by the endangered pygmy blue tongue lizard tiliqua adelaidensis scincidae
Wildlife Research, 2003Co-Authors: Tim Milne, Michael C Bull, Mark N HutchinsonAbstract:The pygmy blue-tongue lizard, Tiliqua adelaidensis, had been considered extinct until its recent rediscovery near Burra in the mid-north of South Australia. The lizards apparently rely on spider Burrows with a single entrance as refuge sites. In this paper we describe observations from all-day video recordings of the entrances of Burrows occupied by lizards on 31 days across the spring and early summer of 1996. The lizards spent most of each day either retreated down the Burrow or basking at the Burrow entrance. Early in the season, when temperatures were cooler, lizards spent more of each day basking, and more of their basking time fully emerged from the Burrow, than later in the season. Results are consistent with the hypothesis that the lizards thermoregulate by moving in and out of the Burrow. Lizards also fed by making short excursions from the Burrow, often to catch passing invertebrate prey, although they also fed on flowers early in spring. Later in the season lizards were more likely to vacate their Burrows for longer times, or to move away from their Burrows, and mating activity was observed when males approached Burrows occupied by females. The observations suggest that pygmy blue-tongue lizards rely heavily on Burrows for many activities, and that any conservation management scheme for this endangered species will rely on maintaining an adequate supply of Burrows.
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Burrow choice by individuals of different sizes in the endangered pygmy blue tongue lizard tiliqua adelaidensis
Biological Conservation, 2000Co-Authors: Tim Milne, Michael C BullAbstract:The pygmy blue tongue lizard Tiliqua adelaidensis had been considered extinct until its recent rediscovery near Burra in the mid-north of South Australia. The lizards apparently rely on spider Burrows as refuge sites. In this paper we describe the dimensions of Burrows occupied by lizards. Larger lizards occupy deeper Burrows with wider entrance diameters than do smaller juvenile lizards. When offered a choice of artificial Burrows in the field, all lizards preferred vertical over angled Burrows, while adult lizards preferred deeper Burrows than did juveniles. In laboratory trials with artificial Burrows of equal depth, lizards tended to prefer the narrowest Burrow they could fit into. We suggest that lizards are constrained by a preference for a deep Burrow to reduce the risk of being dug out, and to avoid climatic extremes, and a preference for a narrow Burrow in which they can block predator access. The result is that smaller lizards have different optimal Burrow dimensions than larger lizards. To maintain a viable population of lizards a variety of Burrow sizes is needed. Conservation strategies for this species may include maintaining a diverse community of hole digging spiders, or providing a variety of sizes of artificial Burrows.
Mark N Hutchinson - One of the best experts on this subject based on the ideXlab platform.
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adding Burrows to enhance a population of the endangered pygmy blue tongue lizard tiliqua adelaidensis
Biological Conservation, 2004Co-Authors: Nicholas J Souter, Michael C Bull, Mark N HutchinsonAbstract:The endangered pygmy blue tongue lizard, Tiliqua adelaidensis, occupies spider Burrows in a population near Burra, South Australia. In each of twelve 20 × 20 m plots at that population, we added 36 artificial Burrows, providing about a ten fold increase in suitable Burrows for lizards. Over three surveys during the spring and summer of 2001/2002 there were significant increases in lizard numbers in the experimental plots relative to the controls, both for adult lizards and for new recruits after clutches were produced. This local increase in population density may be due to lizards locating suitable Burrows more easily where Burrow numbers were supplemented. The increased availability of high quality Burrows may also reduce mortality among lizards searching for suitable Burrows. Additional Burrows also led to an increase in local density of a Burrow-dwelling centipede that is a potential predator of lizards, but there was no evidence of predation, and any negative predation impact was outweighed by the beneficial effect of providing more Burrows. Overall the results suggest that adding artificial Burrows could enhance local population density and recruitment success, and that this could be a valuable tool in the conservation management of this endangered species.
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use of Burrows by the endangered pygmy blue tongue lizard tiliqua adelaidensis scincidae
Wildlife Research, 2003Co-Authors: Tim Milne, Michael C Bull, Mark N HutchinsonAbstract:The pygmy blue-tongue lizard, Tiliqua adelaidensis, had been considered extinct until its recent rediscovery near Burra in the mid-north of South Australia. The lizards apparently rely on spider Burrows with a single entrance as refuge sites. In this paper we describe observations from all-day video recordings of the entrances of Burrows occupied by lizards on 31 days across the spring and early summer of 1996. The lizards spent most of each day either retreated down the Burrow or basking at the Burrow entrance. Early in the season, when temperatures were cooler, lizards spent more of each day basking, and more of their basking time fully emerged from the Burrow, than later in the season. Results are consistent with the hypothesis that the lizards thermoregulate by moving in and out of the Burrow. Lizards also fed by making short excursions from the Burrow, often to catch passing invertebrate prey, although they also fed on flowers early in spring. Later in the season lizards were more likely to vacate their Burrows for longer times, or to move away from their Burrows, and mating activity was observed when males approached Burrows occupied by females. The observations suggest that pygmy blue-tongue lizards rely heavily on Burrows for many activities, and that any conservation management scheme for this endangered species will rely on maintaining an adequate supply of Burrows.
Tim Milne - One of the best experts on this subject based on the ideXlab platform.
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use of Burrows by the endangered pygmy blue tongue lizard tiliqua adelaidensis scincidae
Wildlife Research, 2003Co-Authors: Tim Milne, Michael C Bull, Mark N HutchinsonAbstract:The pygmy blue-tongue lizard, Tiliqua adelaidensis, had been considered extinct until its recent rediscovery near Burra in the mid-north of South Australia. The lizards apparently rely on spider Burrows with a single entrance as refuge sites. In this paper we describe observations from all-day video recordings of the entrances of Burrows occupied by lizards on 31 days across the spring and early summer of 1996. The lizards spent most of each day either retreated down the Burrow or basking at the Burrow entrance. Early in the season, when temperatures were cooler, lizards spent more of each day basking, and more of their basking time fully emerged from the Burrow, than later in the season. Results are consistent with the hypothesis that the lizards thermoregulate by moving in and out of the Burrow. Lizards also fed by making short excursions from the Burrow, often to catch passing invertebrate prey, although they also fed on flowers early in spring. Later in the season lizards were more likely to vacate their Burrows for longer times, or to move away from their Burrows, and mating activity was observed when males approached Burrows occupied by females. The observations suggest that pygmy blue-tongue lizards rely heavily on Burrows for many activities, and that any conservation management scheme for this endangered species will rely on maintaining an adequate supply of Burrows.
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Burrow choice by individuals of different sizes in the endangered pygmy blue tongue lizard tiliqua adelaidensis
Biological Conservation, 2000Co-Authors: Tim Milne, Michael C BullAbstract:The pygmy blue tongue lizard Tiliqua adelaidensis had been considered extinct until its recent rediscovery near Burra in the mid-north of South Australia. The lizards apparently rely on spider Burrows as refuge sites. In this paper we describe the dimensions of Burrows occupied by lizards. Larger lizards occupy deeper Burrows with wider entrance diameters than do smaller juvenile lizards. When offered a choice of artificial Burrows in the field, all lizards preferred vertical over angled Burrows, while adult lizards preferred deeper Burrows than did juveniles. In laboratory trials with artificial Burrows of equal depth, lizards tended to prefer the narrowest Burrow they could fit into. We suggest that lizards are constrained by a preference for a deep Burrow to reduce the risk of being dug out, and to avoid climatic extremes, and a preference for a narrow Burrow in which they can block predator access. The result is that smaller lizards have different optimal Burrow dimensions than larger lizards. To maintain a viable population of lizards a variety of Burrow sizes is needed. Conservation strategies for this species may include maintaining a diverse community of hole digging spiders, or providing a variety of sizes of artificial Burrows.
Nicholas J Souter - One of the best experts on this subject based on the ideXlab platform.
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adding Burrows to enhance a population of the endangered pygmy blue tongue lizard tiliqua adelaidensis
Biological Conservation, 2004Co-Authors: Nicholas J Souter, Michael C Bull, Mark N HutchinsonAbstract:The endangered pygmy blue tongue lizard, Tiliqua adelaidensis, occupies spider Burrows in a population near Burra, South Australia. In each of twelve 20 × 20 m plots at that population, we added 36 artificial Burrows, providing about a ten fold increase in suitable Burrows for lizards. Over three surveys during the spring and summer of 2001/2002 there were significant increases in lizard numbers in the experimental plots relative to the controls, both for adult lizards and for new recruits after clutches were produced. This local increase in population density may be due to lizards locating suitable Burrows more easily where Burrow numbers were supplemented. The increased availability of high quality Burrows may also reduce mortality among lizards searching for suitable Burrows. Additional Burrows also led to an increase in local density of a Burrow-dwelling centipede that is a potential predator of lizards, but there was no evidence of predation, and any negative predation impact was outweighed by the beneficial effect of providing more Burrows. Overall the results suggest that adding artificial Burrows could enhance local population density and recruitment success, and that this could be a valuable tool in the conservation management of this endangered species.
Francesca Gherardi - One of the best experts on this subject based on the ideXlab platform.
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factors inducing the intense Burrowing activity of the red swamp crayfish procambarus clarkii an invasive species
Naturwissenschaften, 2004Co-Authors: Silvia Barbaresi, Elena Tricarico, Francesca GherardiAbstract:The Burrowing activity of the invasive red-swamp crayfish, Procambarus clarkii, was studied along a 25-m-long transect in an irrigation ditch system in Italy. Our objective was to understand the factors inducing this species’ intense digging, which can result in bank collapse and consequently in severe damage to both agricultural fields and natural ecosystems. Burrow morphology and position, together with their occupancy by crayfish and digging, were recorded once every 6 h for 10 consecutive days. The majority of Burrows were simple, although a few had a chimney and were constructed at a farther distance from the water surface than simple Burrows. Burrow occupancy and digging, together with their plugged/unplugged status, were constant throughout a 24-h cycle and were not related to any abiotic parameter of the habitat. Crayfish occupied and dug a Burrow for a relatively short time (6 h on average). Once abandoned, old Burrows were rarely reoccupied and often collapsed, while crayfish excavated new ones. As a result, the overall number of Burrows increased. This massive use of banks by P. clarkii seems to be related to soil composition and humidity, which favour crayfish digging but also cause the easy collapse of Burrows.
